Recom + Caps? or alone? Highly fluctuating V input...

Discussion in 'General Electronics Chat' started by bob332, May 6, 2011.

  1. bob332

    Thread Starter Member

    Feb 14, 2011
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    using a 5V/1A recom over a 780X for simplicity and efficiency. have used this circuit in the past with good results for alternative uses but thought it would work well for this project with the recom:
    [​IMG]

    i understand the V listed on the circuit is a bit off, but that is just for reference at this point. also will probably change the 1n4004 to a 1n4148, other than that, please lmk your thoughts taking into the following conditions:

    i have noticed that the recom datasheets do not recommend any caps at all but i am assuming they are expecting a relatively stable V, my input power will be bouncing all over the place between 9.5V-12.6V constantly and don't know how that will effect the recom vs a regular 780X and if caps should be around the recom due to that fluctuating incoming V.

    this will be going on a radio controlled multirotor distribution board that powers an arduino, rx for the radio gear, video tx (1.2 (not yet, in the future) and/or 5.8GHz, 20mW for now, up to 500mW later) and 5V camera. on a side question, should i put some caps before the pins for the vtx/camera also or since the V @ 5V will be regulated, is it a non issue? either way, it is not an issue so please let me know the best way with what i have described. i would like to keep everything running off the main lipo and not run multiple batts, that is very important.

    i will tap off this 5V output and use a 3V3 (ti tps71733) ldo reg to power the sensor board which consists of a 3axis gyro, 3axis accel (and possibly 3axis mag and barometer in the future).

    here is the ds for the recom, going with the 5V unit:
    http://www.recom-international.com/pdf/Innoline/R-78xx-1.0.pdf

    thanks in advance for your time and advice,
    bob
     
    Last edited: May 8, 2011
  2. bob332

    Thread Starter Member

    Feb 14, 2011
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    anybody have any input on this?
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    The out put cap is too high, it should be around 10uf
     
  4. bob332

    Thread Starter Member

    Feb 14, 2011
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    thanks, anybody else?
     
  5. bob332

    Thread Starter Member

    Feb 14, 2011
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    any other input? i would like to get as much feedback as possible before i have the proto boards made.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I guess tht's it.
    Those values are what I always use.
     
  7. bob332

    Thread Starter Member

    Feb 14, 2011
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    0
    thanks :)

    since i am going to break out some pins that will also power a 5V video tx and camera, should i put a 100nF ceramic before the pins for that output to get it as clean as possible? i think i need to hit up craigslist for an older o-scope to see exactly what i am getting w/ the noise in the power lines, but until then, would the 100nF ceramics be ok to power a video setup or should i use a different value? and should it be ceramic, tantalum or electrolytic?

    any links would be welcome as i don't have a problem learning on my own, just the google lottery sometimes returns not-so-helpful results.

    thanks again.
     
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